The present invention relates to lithium nickel manganese cobalt composite oxide and a lithium rechargeable battery superior in rate characteristics and cycle characteristics.
In recent years, there is a rapidly growing demand for a non-aqueous system lithium rechargeable battery as a high energy density battery. This lithium rechargeable battery is configured from three fundamental components; namely, a positive electrode, a negative electrode, and a separator retaining an electrolyte interposed between these electrodes.
As the positive electrode and negative electrode, a slurry obtained by mixing and dispersing active materials, conductive materials, bonding materials and plasticizing agents (where appropriate) in a dispersion medium is used by being supported by a collector such as a metallic foil or a metallic mesh.
Among the above, a composite oxide of lithium and transition metal is used as the positive electrode active material as represented by cobalt composite oxide, nickel composite oxide, and manganese composite oxide. These lithium composite oxides are generally synthesized by mixing the compound of the main element (carbonate or oxide of Mn, Fe, Co, Ni and the like) and the lithium compound (lithium carbonate and the like) at a prescribed ratio, and subjecting this to heat treatment (oxidation treatment) (refer to Patent Document 1, Patent Document 2 and Patent Document 3).
Under these circumstances, proposed is a ternary positive electrode material having a composition of Ni:Mn:Co=1:1:1 (refer to Patent Document 4). Patent Document 4 describes that it is able to obtain a Li/metal ratio of 0.97 to 1.03 and a discharged capacity of 200 mAh/g. However, this is obtained as a result of the charged final voltage being a high voltage at 4.7V, and if the voltage is cut at 4.3V, the initial discharged capacity will be roughly 150 mAh/g.
Generally speaking, the initial characteristics, the cycle characteristics or the internal resistance of a battery differ significantly depending on the crystal structure of the material. Even if the battery has a layered structure, there is a problem in that the spinel structure that coexists locally will lead to the deterioration of the battery characteristics.
Thus, the identification of the crystal structure is important. Conventionally, XRD (X-ray diffraction method) has been used for the identification of the crystal structure. Nevertheless, it was difficult to assess the coexistence of phases due to the peak positions being near or other reasons.
Accordingly, a proposal has been made for specifying the cathode active material with Raman spectroscopy (refer to Patent Document 5). Although Patent Document 5 specifies the peak intensity ratio of the spinel structure and the hexagonal crystal structure in the Raman spectrum analysis of the chemical formula LiCoMA2 (0.95≦Li≦1.0, A includes O, F, S and P), the main peak is the peak of the spinel structure and, since it is not a layered structure, it cannot be said that sufficient characteristics are being obtained.
As described above, although a lithium rechargeable battery material possesses superior characteristics in comparison to conventional technology, further improvement is demanded with respect to sinterability and battery characteristics.
[Patent Document 1] Japanese Patent Laid-Open Publication No. H1-294364
[Patent Document 2] Japanese Patent Laid-Open Publication No. H11-307094
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-285572
[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-59490
[Patent Document 5] Japanese Patent Laid-Open Publication No. 2005-44785